There is a requirement in a number of machines to provide cooling in order to retain the machine within acceptable operating temperatures. Typically, air or a liquid coolant is used to effectively transport heat energy from a hot region and allow it to be conventionally dispersed. Clearly, the rates of coolant flow and interface with the machine are highly determinant of the effectiveness of a coolant.
FIG. 1 in the attached drawings shows a turbine blade 1 typical of those used in a jet engine. High pressure cooling air passes through the turbine blade 1 in the direction of arrowheads A whilst low pressure cooling air passes through blade 1 in the direction of arrowheads B. In any event, the air flows in the turbine blade 1 for appropriate dispersion. Normally, the high pressure air flow in accordance with arrowheads A is towards the leading edge of the blade 1 where there will be most heating of the blade 1.
It will be appreciated that a higher level of cooling for the blade 1 is required at certain stages of engine activity, for example take off, in comparison with normal operation, for example cruising at altitude. In such circumstances, provision of air coolant through the blade 1 in a permanently open flow matrix 2 results in the engine not necessarily being operated at its optimum efficiency. It will be noted that the engine may be designed to vary the rate of air flow through the matrix 2, but this will generally be related to engine speed rather than desired cooling for engine activity.